In order to analyze surface crack effects on SRM grain structural integrity,the-50℃ ignition test was conducted for the SRM with preseted inner surface crack which was 0. 6 mm in depth. At the same time cracks with various depths in the SRM grain were preseted firstly. Then J integral of cracks was respectively calculated based on finite element method. With the engineering case analysis,fracture toughness and the ultimate value of J resistance were obtained under-50℃ ignition test. The results show that the structural integrity of grain was even worse under such conditions,which means the surface cracks growing easily,but the cracks could arrest when reached the shell.